You can usually buy balsamic glaze at a grocery store, but if not, here is a great recipe (source):

Combine 1 cup balsamic vinegar, 2 tablespoons brown sugar and 1 tablespoon soy sauce in a small saucepan and bring to a boil. Reduce heat to low and simmer until thick and syrupy, about 20 minutes. Remove from heat and let cool.

You might notice that the picture is missing olive oil. I realized halfway through eating this that it was missing something. So I added 1 tablespoon of olive oil, and it made the dish complete, as well as 100 times better.